egrep understanding problem

Hi,
Can anyone please let me know the meaning of this line,i am not able to understand the egrep part(egrep '^[0-9]{1,2}).This will search for this combination in beginning but what does the values in {}signifies here.

/bin/echo $WhenToRun | egrep '^[0-9]{1,2}:[0-5][0-9]$' >/dev/null

Please use the man pages when you can

From man egrep.

       A  regular  expression  may  be  followed by one of several repetition
       operators:
       ?      The preceding item is optional and matched at most once.
       *      The preceding item will be matched zero or more times.
       +      The preceding item will be matched one or more times.
       {n}    The preceding item is matched exactly n times.
       {n,}   The preceding item is matched n or more times.
       {n,m}  The preceding item is matched at least n times,  but  not  more
              than m times.

  1. 0-9 ↩︎

  2. 0-9 ↩︎